1. Field of the Present Invention
The present invention relates to semiconductor devices, and more particularly, to the use of thin films of nanowires in semiconductor devices for various applications.
2. Background Art
An interest exists in industry in developing low cost electronics, and in particular, in developing low cost, large area macroelectronic devices. Large-area macroelectronics is defined as the implementation of active and sensory electronic components over a large surface area. Here, a large area is not used to fit all of the electronic components, but rather because such systems must be physically large to realize improved performance and the active components of such systems must be distributed over the large area to realize a useful functionality. The incorporation of active devices over a large common substrate is driven by system performance, reliability, and cost factors, not necessarily by individual component performance. Such large area macroelectronic devices could revolutionize a variety of technology areas, ranging from civilian to military applications. Example applications for such devices include driving circuitry for active matrix liquid crystal displays (LCDs) and other types of matrix displays, smart libraries, credit cards, radio-frequency identification (RFID) tags for smart price and inventory tags, security screening/surveillance or highway traffic monitoring systems, large area sensor arrays, and the like.
Current approaches involve using amorphous silicon or polysilicon as the base materials for thin-film transistors (TFTs). Organic semiconductors are emerging as an alternative. However, amorphous silicon and organic semiconductors have performance limitations. For example, they exhibit low carrier mobility, typically about 1 cm2/V·s (centimeter squared per volt second) or less. Polysilicon has showed improved performance, but requires relatively expensive processes, such as laser induced annealing, and is incompatible with low temperature substrates, such as cheap glass and plastics.
Unfortunately, traditional electronic materials are characterized by a roughly inverse relationship between electronic performance (determined primarily by carrier mobility, μ) and available substrate size. FIG. 1 is a plot that schematically illustrates materials performance (mobility) vs. available substrate size for different semiconductor materials. Traditional materials either have high performance but small substrate sizes (e.g., GaAs), or larger sizes with low performance (e.g., amorphous silicon or organics). Current electronic materials can only access the most primitive large-area macroelectronics applications. This leaves a tremendous void in materials characteristics, which has prevented the development of the highest-value macroelectronic applications, such as wearable communications and electronics, distributed sensor networks, and radio frequency (RF) beam-steering systems, to name a few.
For instance, to realize a beam-steering reflector for use within a space-fed antenna system, the steering-element circuits would have to be distributed across the entire reflector, each with extreme performance requirements typically associated with high-mobility InAs substrates. InAs wafers, however, are currently limited to a maximum of 3–4 inches (8–10 cm) in diameter and are extremely brittle, making them inappropriate for use in such large-area distributed electronic circuits. As such, the only methods currently available for fabricating such large-area circuits are to wire-bond or solder discrete transistors and components on the large-area active reflector, a costly and failure-prone alternative with inherent performance and efficiency limitations. Today, even military applications of such arrays are limited to such examples as solid communications arrays on Navy destroyers; they cannot be implemented into mobile, let alone man-portable, communications systems.
Accordingly, what is needed are higher performance conductive or semiconductive materials and devices, electronic substrate materials, and methods and systems for producing lower-cost, high performance electronic devices and components. Preferably, such materials would be readily available, cost effectively manufactured, and enjoy other advantages with regards to weight, flexibility, and the like.
Many applications can benefit from such higher performance conductive semiconductive materials, including acoustic cancellation and RF identification (RFID) tag/reader applications. In RFID tag applications, a device known as a “tag” may be affixed to items or objects that are to be monitored. The presence of the tag, and therefore the presence of the item to which the tag is affixed, may be checked and monitored by devices known as “readers.” A reader may monitor the existence and location of the items having tags affixed thereto through wireless interrogations. Typically, each tag has a unique identification number that the reader uses to identify the particular tag and item.
A limiting factor in the area of RFID tag tracking systems is the cost of the tags. Further limiting factors include the distance between the reader and tags, and the orientation of tag antennas relative to the reader antenna. If a tag antenna is not oriented properly relative to the reader antenna, the tag must be close to the reader to be detected.
These limiting factors are critical when attempting to read multiple tags affixed to items within a container that is in transit from one location to another. For example, a shipping truck may pass through a checkpoint at 60 mph. If the truck is transporting a large number of tagged items, such as tens or hundreds of thousands of items, the truck must be within a reader's range long enough to detect all of the tags. If each item within the container on the truck is randomly oriented, causing a maximum read distance for the container to be low, the reader may only have a few seconds to read all of the tags. Current tag and reader technology is not capable of reading such a large number of items in a few seconds.
Thus, what is also needed are methods and systems for increasing a read rate for tags, for increasing a distance over which the tags may be read, and for lower cost tags.
In acoustic cancellation applications, an attempt is made to cancel or reduce specific frequencies of sound, such as the cancellation or reduction of noise. For example, in some instances it may be desirable to partially or completely cancel the sound emanating from objects such as a car, a bus, or even an airplane. In military applications, it may be desirable to partially or completely cancel sounds from objects such as a tank or submarine. Some conventional headphones incorporate technology that monitors noise around the headphones, and transmits a pattern of acoustic waves in an attempt to substantially cancel the outside noise. The transmitted pattern of acoustic waves is transmitted with an opposite phase to that of the noise. This transmitted pattern attempts to silence the noise, making it easier to hear what is being played through the headphones. However, such technology is limited to relatively small size devices, such as headphones, and cannot be applied to the large objects mentioned above.
Thus, what is further needed are methods and systems for performing acoustic cancellation that effectively operate to cancel sounds and/or noise over any size area, including large areas.